The present invention generally relates to wireless communication networks, and particularly relates to reverse link load management in such networks.
Wireless networks based on Code Division Multiple Access (CDMA) technology are termed “interference limited” networks because the number of users that can be simultaneously supported is limited by the prevailing interference. This limitation particularly applies to the “reverse link” from the mobile stations to a network Base Station (BS). The BS must receive each mobile station's reverse link signals at a sufficient Signal-to-Noise (SNR) for reliable decoding and thus the BS commands individual mobile stations to increase or decrease their transmit powers to maintain the targeted SNRs. However, the available transmit power at each mobile station is relatively limited, and, because each mobile station's transmit power contributes to overall interference, the BS must control the transmit powers of all mobile stations to maintain overall interference at tolerable levels.
In networks that support variable data rates on the reverse link, the level of reverse link interference can be managed at least in part by adjusting the data rates of the individual mobile stations upward or downward, which results in commensurate increases or decreases in the transmit power required from each mobile station to achieve the targeted received signal quality at the BS. The reverse packet data channels (R-PDCHs) defined in the developing IS-2000 standards exemplify the type of reverse link rate-controlled channels that may be adjusted as a function of reverse link loading (interference).
One approach to such adjustment is termed Common Rate Control (CRC), wherein the BS broadcasts rate control commands that are followed by the plurality of mobile stations being served by that BS. The rate control commands typically are broadcast on a per frame basis, which may be every 10 ms, every 20 ms, or at whatever value corresponds to the defined reverse link frame timing. One characteristic of the CRCs is that they do not set specific reverse link data rates at each mobile station, but rather provide generally applicable up, down, or, in some networks, hold indications to be followed by the mobile stations. Thus, different mobile stations operating at different reverse link data rates would each drop to the next lower rate relative to the current rate in response to receiving a generally broadcast down command, or would each step up to the next higher rate relative to the current rate in response to receiving a generally broadcast up command.
With the CRC-based approach, then, the BS commands the mobile stations it is supporting to move their reverse link data rates incrementally up and down as needed responsive to changing reverse link loading levels. However, this common rate control approach does not address the desire of network operators to pursue particular service objectives, such as fairness or throughput-based objectives, nor does it necessarily achieve effective utilization of the available reverse link capacity.